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F   UID   PID  PPID PRI  NI   VSZ  RSS WCHAN  STAT TTY        TIME COMMAND
0  1013 20591 20590  15   0  9224 2696 rt_sig Ss   pts/1      0:00 -tcsh
0  1013 20761 20591  16   0  3724  904 finish T    pts/1      0:00 nm /usr/lib/l
0  1013 20762 20591  16   0  2720  624 finish T    pts/1      0:00 lv
0  1013 20795 20591  16   0  4256  628 -      R+   pts/1      0:00 ps l
$

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$ echo $$ 
23069
$ ls /proc/$$ 
attr             cpuset   fd        maps        numa_maps  schedstat  status
auxv             cwd      io        mem         oom_adj    smaps      task
cmdline          environ  limits    mounts      oom_score  stat       wchan
coredump_filter  exe      loginuid  mountstats  root       statm
$ head -11 /proc/$$/status  
Name:   bash
State:  S (sleeping)
SleepAVG:       98%
Tgid:   23069
Pid:    23069
PPid:   23068
TracerPid:      0
Uid:    1013    1013    1013    1013
Gid:    510     510     510     510
FDSize: 256
Groups: 20 510 1020 1065 1150 
$

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   1:	/*
   2:	        fork-pid.c -- fork() $B$7$F2hLL$K(B pid $B$rI=<($9$k%W%m%0%i%`(B
   3:	        ~yas/syspro/proc/fork-pid.c
   4:	        Created on: 2010/12/13 21:19:17
   5:	*/
   6:	
   7:	#include <sys/types.h>  /* getpid(), getppid() */
   8:	#include <unistd.h>     /* getpid(), getppid() */
   9:	#include <stdio.h>
  10:	
  11:	main()
  12:	{
  13:	    pid_t pid;
  14:	        fork();
  15:	        pid = getpid();
  16:	        printf("pid=%d\n", pid );
  17:	}

$ make fork-pid 
cc     fork-pid.c   -o fork-pid
$ ./fork-pid 
pid=11041
pid=11040
$ ./fork-pid 
pid=11042
pid=11043
$

fork() $B$O!"(BUnix $B$G%W%m%;%9$r@8@.$9$k%7%9%F%`!&%3!<%k!#(B $B%W%m%;%9$r%3%T!<$9$k$3$H$G@8@.$9$k!#(B
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   1:	/*
   2:	        proc-pid-ppid.c -- $B2hLL$K(B pid $B$H(B ppid $B$rI=<($9$k%W%m%0%i%`(B
   3:	        ~yas/syspro/proc/proc-pid-ppid.c
   4:	        Created on: 2010/12/13 21:00:48
   5:	*/
   6:	
   7:	#include <sys/types.h>  /* getpid(), getppid() */
   8:	#include <unistd.h>     /* getpid(), getppid() */
   9:	#include <stdio.h>
  10:	
  11:	main()
  12:	{
  13:	    pid_t pid, ppid;
  14:	        pid = getpid();
  15:	        ppid = getppid();
  16:	        printf("pid=%d, ppid=%d\n", pid, ppid );
  17:	}

$ make proc-pid-ppid 
cc     proc-pid-ppid.c   -o proc-pid-ppid
$ echo $$ 
10771
$ ./proc-pid-ppid  
pid=10873, ppid=10771
$ ./proc-pid-ppid  
pid=10874, ppid=10771
$ ./proc-pid-ppid  
pid=10875, ppid=10771
$

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   1:	/*
   2:	        fork-hello.c -- $B2hLL$KJ8;zNs$rI=<($9$k%W%m%0%i%`(B
   3:	        ~yas/syspro/proc/fork-hello.c
   4:	        Start: 2001/05/13 23:19:01
   5:	*/
   6:	
   7:	#include <stdio.h>
   8:	
   9:	main()
  10:	{
  11:	        fork();
  12:	        fork();
  13:	        fork();
  14:	        printf("hello\n");
  15:	}

$ make fork-hello 
cc     fork-hello.c   -o fork-hello
$ ./fork-hello  
hello
hello
hello
hello
hello
hello
hello
hello
$

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$ id 
uid=1013(yas) gid=510(prof) groups=20(games),510(prof),1020(c-admin),1065(c-spec),1150(tebiki)
$

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id $B%3%^%s%I$O!"FbItE*$K$O(Bgetuid(), getgid(), getgroups() $B%7%9%F%`!&%3!<(B $B%k$r;H$C$F$$$k!#0J2<$O!"(Bid $B%3%^%s%I$N4J0WHG$G$"$k!#(B

   1:	
   2:	/*
   3:	        id-simple.c -- a simple id command
   4:	        Created on: 2009/12/07 22:16:23
   5:	*/
   6:	
   7:	#include <unistd.h>     /* getuid(), getgid(), getgroups() */
   8:	#include <sys/types.h>  /* getuid(), getgid(), getgroups() */
   9:	#include <stdio.h>      /* printf() */
  10:	
  11:	#define MAXNGROUPS 100
  12:	
  13:	main( int argc, char *argv[], char *envp[] )
  14:	{
  15:	    uid_t uid ;
  16:	    gid_t gid ;
  17:	    gid_t groups[MAXNGROUPS];
  18:	    int len, i;
  19:	        uid = getuid();
  20:	        gid = getgid();
  21:	        len = getgroups(MAXNGROUPS,&groups[0]);
  22:	        printf("uid=%d gid=%d groups=", uid, gid );
  23:	        for( i=0; i<len; i++ )
  24:	            printf("%d,", groups[i]);
  25:	        printf("\n");
  26:	}

$ cc id-simple.c -o id-simple 
$ ./id-simple 
uid=1013 gid=510 groups=20,510,1020,1065,1150,
$

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1163:	struct task_struct {
1164:	        volatile long state;    /* -1 unrunnable, 0 runnable, >0 stopped */
...
1224:	        int exit_state;
...
1251:	        struct task_struct *real_parent; /* real parent process */
1252:	        struct task_struct *parent; /* recipient of SIGCHLD, wait4() reports */
1253:	        /*
1254:	         * children/sibling forms the list of my natural children
1255:	         */
1256:	        struct list_head children;      /* list of my children */
1257:	        struct list_head sibling;       /* linkage in my parent's children list */
1258:	        struct task_struct *group_leader;       /* threadgroup leader */
...
1268:	        /* PID/PID hash table linkage. */
1269:	        struct pid_link pids[PIDTYPE_MAX];
1270:	        struct list_head thread_group;
...
1290:	/* process credentials */
1291:	        const struct cred *real_cred;   /* objective and real subjective task
1292:	                                         * credentials (COW) */
1293:	        const struct cred *cred;        /* effective (overridable) subjective task
1294:	                                         * credentials (COW) */
...
1300:	        char comm[TASK_COMM_LEN]; /* executable name excluding path
1301:	                                     - access with [gs]et_task_comm (which lock
1302:	                                       it with task_lock())
1303:	                                     - initialized normally by setup_new_exec */
...
1497:	};

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 182:	#define TASK_RUNNING            0
 183:	#define TASK_INTERRUPTIBLE      1
 184:	#define TASK_UNINTERRUPTIBLE    2
 185:	#define __TASK_STOPPED          4
 186:	#define __TASK_TRACED           8
 187:	/* in tsk->exit_state */
 188:	#define EXIT_ZOMBIE             16
 189:	#define EXIT_DEAD               32
 190:	/* in tsk->state again */
 191:	#define TASK_DEAD               64
 192:	#define TASK_WAKEKILL           128
 193:	#define TASK_WAKING             256
 194:	#define TASK_STATE_MAX          512

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$B"!(Bpids[]

pids[] $B$O!"%W%m%;%9<1JL;R$rJ];}$9$k$?$a$NG[Ns!#$$$/$D$+$Ngetpid(),getppid(),fork() $B$K4XO"$7$F$$$k$b$N$O!"(B0 $BHVL\(B $B$N(B pids[PIDTYPE_PID]$B!#(B

pids[PIDTYPE_PID] $B$O!"(Bpid_link $B7?$G!"FbIt$K(Bstruct pid $B$r;}$D!#(Bstruct pid $B$NCf$K$O!"(Bstruct upid $B$,$"$j!"$=$NCf$K$O(B getpid() $BEy$GMQ$$$k(B pid $B$r(B $BJ];}$9$k%U%#!<%k%I(B nr $B$,$"$k!#(B

include/linux/pid.h
  50:	struct upid {
...
  52:	        int nr;
...
  55:	};
  57:	struct pid
  58:	{
...
  64:	        struct upid numbers[1];
  65:	};
...
  69:	struct pid_link
  70:	{
...
  72:	        struct pid *pid;
  73:	};

$B"!(Bchar comm[TASK_COMM_LEN]

command$BL>!#:GBg(B16$BJ8;z!#(B

$B"!%W%m%;%9$NLZ9=B$(B

real_parent, children, sibling $B$H$$$&%U%#!<%k%I$G%W%m%;%9$NLZ9=B$$,:n$i$l$k!#(B

$B?^(B? $B%W%m%;%9$NLZ9=B$(B

$B"!(Bstruct task_struct *real_parent

$B?F%W%m%;%9(B(fork() $B%7%9%F%`!&%3!<%k$G%3%T!<85$N%W%m%;%9!#(B)$B$N(Btask_struct$B9=B$BN$X$N%]%$%s%?!#(B $B?F$,@h$K;`$s$@>l9g$K$O!"(Binit$B%W%m%;%9$KM\;R$K=P$5$l$k!#(B

$B"!(Bstruct task_struct *parent

ptrace $B$G!"%H%l!<%9$7$F$$$k%W%m%;%9(B($B%G%P%C%,Ey(B)$B!#(B

$B"!(Bstruct list_head children

$B;R%W%m%;%9$N%j%9%H$N@hF,!#(B

$B"!(Bstruct list_head sibling

$B7;Do%W%m%;%9!J$D$^$j!"F1$8?F%W%m%;%9$N;R%W%m%;%9!K$N%j%9%H!#(B

$B"!(Bstruct cred *real_cred

credentials$B!#;q3J!#%U%!%$%k$r%"%/%;%9$9$k;~Ey$K%W%m%;%9$,$I$N$h$&$J8"8B(B $B$r;}$C$F$$$k$+$rI=$9!#(B

$B?^(B? UID$B$NJ]B8J}K!(B

$B"!(Bstruct cred

task_struct $B$KJ]B8$9$Y$-FbMF$N$&$A!"(Buid$B!"(Bgid$B!"(Bgroups $BEy$rH4$-=P$7$?$b$N!#(B

include/linux/cred.h

  25:	/*
  26:	 * COW Supplementary groups list
  27:	 */
  28:	#define NGROUPS_SMALL           32
  29:	#define NGROUPS_PER_BLOCK       ((unsigned int)(PAGE_SIZE / sizeof(gid_t)))
  30:	
  31:	struct group_info {
  32:	        atomic_t        usage;
  33:	        int             ngroups;
  34:	        int             nblocks;
  35:	        gid_t           small_block[NGROUPS_SMALL];
  36:	        gid_t           *blocks[0];
  37:	};
...
 116:	struct cred {
 117:	        atomic_t        usage;
 118:	#ifdef CONFIG_DEBUG_CREDENTIALS
 119:	        atomic_t        subscribers;    /* number of processes subscribed */
 120:	        void            *put_addr;
 121:	        unsigned        magic;
 122:	#define CRED_MAGIC      0x43736564
 123:	#define CRED_MAGIC_DEAD 0x44656144
 124:	#endif
 125:	        uid_t           uid;            /* real UID of the task */
 126:	        gid_t           gid;            /* real GID of the task */
 127:	        uid_t           suid;           /* saved UID of the task */
 128:	        gid_t           sgid;           /* saved GID of the task */
 129:	        uid_t           euid;           /* effective UID of the task */
 130:	        gid_t           egid;           /* effective GID of the task */
...
 148:	        struct user_struct *user;       /* real user ID subscription */
 149:	        struct group_info *group_info;  /* supplementary groups for euid/fsgid */
...
 151:	};

$B"!(Buid$B$H(Bgid

uid$B$O!"%f!<%6$r<1JL$9$kHV9f!"(Bgid$B$O!"%0%k!<%W$r<1JL$9$kHV9f$rJ];}$9$k!#(B $B%U%!%$%k$r3+$/;~Ey$N%"%/%;%98"$N%A%'%C%/$K;H$o$l$k!#(B

$B"!(Beuid$B$H(Begid

effective uid $B$H(B effective gid$B!#(B

Unix $B$K$O!"(Bset-uid $B$N%W%m%0%i%`$,$"$k!#(Bls -l $B$G(B user $B$N(B x $B$N=j$,(B s $B$K$J$C(B $B$F$$$k!#(B

$ ls -l /usr/bin | egrep '^...s' 
...
-rwsr-xr-x 1 root root       49392 Jan 27  2010 at
...
-rwsr-sr-x 1 root root      315432 Jan  6  2010 crontab
-rwsr-xr-x 1 root root       51576 Mar 31  2010 gpasswd
...
---s--x--x 2 root root      180448 Oct 19 22:11 sudo
...
$

$B$3$N$h$&$J%W%m%0%i%`$r$B"!(Bgroup_info $BDI2C$N(Bgid (getgroups()) $B$rJ];}$9$k!#(B

$B"#(Bcurrent

$BJQ?t(B current $B$O!"%+!<%M%kCf$G8=:_H$9$k!#(B

$B"!(Bgetpid()$B%7%9%F%`!&%3!<%k(B

kernel/timer.c

1351:	SYSCALL_DEFINE0(getpid)
1352:	{
1353:	        return task_tgid_vnr(current);
1354:	}

include/linux/sched.h
1600:	static inline pid_t task_tgid_vnr(struct task_struct *tsk)
1601:	{
1602:	        return pid_vnr(task_tgid(tsk));
1603:	}

1538:	static inline struct pid *task_tgid(struct task_struct *task)
1539:	{
1540:	        return task->group_leader->pids[PIDTYPE_PID].pid;
1541:	}

getpid() $B%7%9%F%`!&%3!<%k$N task_tgid() $B$G$O!"(B(group_leader $B$N(B) pids[PIDTYPE_PID].pid (struct pid *$B7?(B)$B$rJV$7$F$$$k!#(B
pid_vnr() $B$O!"(Bstruct pid *$B$r(Bpid_t (int$B7?(B) $B$XJQ49$9$k!#(B

group_leader $B$O!"%f!<%6%l%Y%k$GF1$8%W%m%;%9$KB0$9$k!"%+!<%M%k!&%l%Y%k$N(B $B%9%l%C%I$N@hF,$N$b$N$r;X$9!#(Bgroup_leader $B$O!"$I$N%+!<%M%k!&%l%Y%k$N%9%l%C(B $B%I$+$iD4$Y$F$b!"F1$8(B struct task_struct $B$r;X$7$F$$$k!#(B


kernel/pid.c
 474:	pid_t pid_vnr(struct pid *pid)
 475:	{
 476:	        return pid_nr_ns(pid, $B>JN,(B);
 477:	}
...
 461:	pid_t pid_nr_ns(struct pid *pid, $B>JN,(B)
 462:	{
 463:	        struct upid *upid;
 464:	        pid_t nr = 0;
...
 467:	                upid = &pid->numbers[$B>JN,(B];
...
 469:	                        nr = upid->nr;
 471:	        return nr;
 472:	}

struct pid $B9=B$BN$+$i(B struct upid $B9=B$BN$r
struct upid $B9=B$BN$N(B nr $B$H$$$&%U%#!<%k%I$r
$B"!(Bgetppid()$B%7%9%F%`!&%3!<%k(B
```
kernel/timer.c
1362:	SYSCALL_DEFINE0(getppid)
1363:	{
1364:	        int pid;
...
1367:	        pid = task_tgid_vnr(current->real_parent);
...
1370:	        return pid;
1371:	}
```
current$B$N(Breal_parent$B$r0z?t$K$7$F(B task_tgid_vnr() $B$H$$$&4X?t$r8F$V!#(B $B0J9_!"(Bgetpid() $B$HF1$8!#(B
$B"!(Bgetuid()$B%7%9%F%`!&%3!<%k(B
```
kernel/timer.c
1373:	SYSCALL_DEFINE0(getuid)
1374:	{
1375:	        /* Only we change this so SMP safe */
1376:	        return current_uid();
1377:	}
```
current_uid() $B$H$$$&4X?t(B($B%^%/%m(B)$B$r8F$S=P$9!#(B
```
include/linux/cred.h

 342:	#define current_cred_xxx(xxx)                   \
 343:	({                                              \
 344:	        current->cred->xxx;                     \
 345:	})
 346:	
 347:	#define current_uid()           (current_cred_xxx(uid))
```
current$B$+$i(Bcred$B$r0z$-!"$=$NCf$N(B uid $B$H$$$&%U%#!<%k%I$rJV$9!#(B
$B"#%/%$%:(B2 $B%W%m%;%9$H(Btask_struct$B9=B$BN(B

$B!zLdBj(B(201) Ready$B>uBV$N%W%m%;%9(B
$B%*%Z%l!<%F%#%s%0!&%7%9%F%`$G$O!"!V0lHL$K!W%W%m%;%9$O!"(BReady$B!"(BRunning$B!"(B Blocked$B$N>uBV$r;}$D!#(BLinux $B$K$*$$$F!"%W%m%;%9$,(B Ready $B>uBV$G$"$k$3$H$r(B $B<($9$?$a$K!"(Btask struct $B$N%U%#!<%k%I(B state $B$K!"2?$H$$$&CM$r@_Dj$7$F$$$k$+!#(B
$B!zLdBj(B(202) pid$B$H(Bppid
$B 1: #include <stdio.h> 2: #include <unistd.h> 3: 4: main() { 5: pid_t pid, ppid; 6: fork(); 7: pid = getpid(); 8: ppid = getppid(); 9: printf("hello: (pid=%d,ppid=%d)\n",pid, ppid); 10: } $B0J2<$N6uMs!J6uMs#A!"6uMs#B!"6uMs#C!"6uMs#D!K$rKd$a$F!"5/$3$jF@$k7k2L$r(B 1$B$D:n$j$J$5$$!#(B
```
$ echo $$ 
1001
$ ./fork-printf  
hello: (pid=$B6uMs#A(B,ppid=$B6uMs#B(B)
hello: (pid=$B6uMs#C(B,ppid=$B6uMs#D(B)
$ 
```
$B$?$@$7!"(BPID $B$H$7$F$O!"(B1001,1002,1003,1004 $B$NCf$+$iA*$S$J$5$$!#(B $B$J$*!"Ez$($O#1DL$j$G$O$J$$!#(B
$B!zLdBj(B(203) getgid()$B%7%9%F%`!&%3!<%k(B
getuid() $B%7%9%F%`!&%3!<%k$K=,$C$F(B getgid() $B%7%9%F%`!&%3!<%k$r
$B%R%s%H(B: current $B$+$i=PH/$9$k!#(Bcurrent_cred_xxx() $B%^%/%m$r;H$C$F$b;H$o$J(B $B$/$F$b$h$$!#(B
Last updated: 2010/12/21 16:47:46

Yasushi Shinjo / <yas@is.tsukuba.ac.jp>